1. Field of the Invention
This invention relates to the stabilization of halogenated butyl rubber and the stabilized compositions resulting therefrom. More particularly, this invention is concerned with stabilization against discoloration at high temperatures of halogenated butyl rubber such as bromochlorinated butyl. Most particularly, this invention relates to said stabilized polymer compositions comprising a halogenated butyl and an effective amount of stabilizer, said stabilizer consisting essentially of an alkali metal or alkaline earth metal carboxylate, an ether and an oxide or hydroxide of a metal selected from Group IIA of the Periodic Table.
Stabilizers are employed in the production of halogenated butyl rubber for such purposes as protecting these polymers from the effects of both high temperatures during manufacture and from long term, moderate temperatures during storage prior to use. Multicomponent systems have been developed to accomplish this task, but deficiencies in such systems have been observed in both actual protection achieved and side effects such as discoloration which can occur with some of the prior art compositions. An object of the present invention is to provide a polymer composition with improved stability.
2. Prior Art
Stabilizers and stabilized polymer compositions in the area of halogenated polymers form a substantial body of prior art. So far as applicants are aware, prior art relevant to stabilization of butyl rubbers is represented by the following disclosures.
U.S. Pat. No. 2,962,473 issued Nov. 29, 1960 to F. P. Baldwin et al is entitled "Process for Stabilizing Halogenated Butyl Rubber Against Gelation With Magnesium Oxide, and Stabilized Product Obtained Thereby." This reference teaches that magnesium oxide can be employed in halogenated butyl rubber, for example, chlorinated isobutylene-isoprene rubber as a stabilizer against gelatin and dehydrohalogenation (col. 1, line 50). The reference fails to teach or suggest the use of other Group IIA metal oxides or hydroxides or the addition of the two additional critical components of the instant invention, the ether and the carboxylate, as will be described in detail in later paragraphs. Furthermore, no information is provided in the reference with regard to stabilization against discoloration of the halogenated butyl rubber compositions containing magnesium oxide. Baldwin et al also describe the use of the stabilized compositions in conventional rubber compositions containing additional fillers and extenders (col. 3, lines 38 ff.), including CaO (line 61), but it was clearly not employed as a critical part of a stabilizer package. The use of adsorbent deactivators such as various high boiling polar compounds (ethylene glycol) is described by Baldwin et al (col. 4, line 7), but the class of materials described and claimed in the instant invention and their critical necessity to the success of the stabilizer composition disclosed herein was not recognized or suggested in the reference. In their preparation of a chlorinated butyl rubber sample Baldwin et al employed "an aliphatic polyoxyethylene ether type wetting agent (i.e. Sterox A.I.)" (col. 5, line 17) in order to obtain an aqueous slurry of the rubber. In the reference this compound was specifically employed as a wetting agent and obviously any other wetting agent would have been satisfactory so long as it maintained the rubber as a slurry. The reference does not teach, suggest or imply that such materials should be retained in the finished rubber or that they might be beneficial for stabilization purposes.
The presence in chlorinated butyl of zinc stearate and the same wetting agent noted above is disclosed in U.S. Pat. No. 2,964,489, "Process of Chlorinating Butyl Rubber and Vulcanizing The Chlorinated Product," issued Dec. 13, 1960, to F. P. Baldwin et al, (column 6, line 56 and column 8, line 67). The reference clearly recites that zinc stearate functions as an "anti-tack agent" (col. 8, line 75) and the aliphatic polyoxyethylene ether functions as a dispersing aid (col. 7, line 61) in precisely the same manner as discussed above. The use of zinc stearate is scrupulously avoided in the instant invention as zinc is an undesirable metal in the presence of halogenated butyl unless one is intentionally attempting to crosslink such polymers. The discussion above relative to the dispersing aid is applicable here too. In addition, the stabilized composition disclosed in the instant invention is not suggested in any form by this reference, the presence of the dispersing agent and the zinc stearate being used merely to facilitate preparation of a stable, processable rubber slurry.
Stabilizers representing only a part of the instant disclosure are described in West German patent Application No. 2,551,040 of K. Tanioka et al published on May 26, 1977. The reference describes stabilizers for polyvinylchloride and other chlorine-containing resins which comprise calcium hydroxide coated with an organic calcium salt, preferably calcium stearate. The method employed to prepare these stabilizers includes the use of a surfactant. Tanioka et al list nonionic, anionic and cationic surfactants as acceptable materials for their process and clearly employ these materials at such levels, and in such a manner so as to function strictly as surfactants, not as critical components of the stabilizer composition. This is emphasized by two factors;
(1) certain ionic surfactants, being water soluble will remain in the water phase during preparation of the coated stabilizer, and
(2) the coated stabilizer will be essentially free of nonionic surfactants in the event an alcohol wash step is used in the process to remove unreacted stearic acid as is shown in Example 1 of the reference. The nonionic surfactants employed are soluble in alcohol and no direction is given to avoid their extraction during preparation of the stabilizer. Therefore, it is obvious that Tanioka et al do not teach, suggest or imply the inclusion of an ether, whereas such a component is specifically disclosed as a critical component in the present invention.
P. Hous, in Belgian Pat. No. 849,943 (1977) and U.S. application Ser. No. 752,886, filed Dec. 21, 1976 now U.S. Pat. No. 4,104,218 issued Aug. 1, 1978 one of the inventors herein has disclosed a stabilizer halobutyl rubber composition comprising a stabilizer consisting essentially of an alkali metal or alkaline earth metal carboxylate, e.g. calcium stearate and an ether, e.g. a polyether. However, this reference fails to teach the advantage disclosed herein of employing a Group IIA metal oxide or hydroxide in combination with the two components noted above. In this connection, attention is invited to Examples 1-4 of the present application.